Even The Biggest Dinosaurs Had Teeny Tiny Brains

An advanced member of the largest group of dinosaurs ever to walk
the Earth still had a relatively puny brain, researchers say.

The scientists analyzed the skull of 70-million-year-old fossils
of the giant dinosaur Ampelosaurus, discovered in 2007
in Cuenca, Spain, in the course of the construction of a
high-speed rail track connecting Madrid with Valencia.

The reptile was a sauropod, long-necked, long-tailed herbivores
that were the largest creatures ever to stride the Earth.

More specifically, Ampelosaurus was a kind of sauropod
known as a titanosaur, many if not all of which had armor-like
scales covering their bodies.

Sauropod skulls are typically fragile, and few have survived
intact enough for scientists to learn much about their brains. By
scanning the interior of the skull via CT imaging, the
researchers developed a 3-D reconstruction of
Ampelosaurus' brain, which was not much bigger than a
tennis ball.

"This saurian may have reached 15 meters (49 feet) in length;
nonetheless its brain
was not in excess of 8 centimeters (3 inches)," study researcher
Fabien Knoll, a paleontologist at Spain's National Museum of
Natural Sciences, said in a statement. [Gallery:
Stunning Illustrations of Dinosaurs]

The first sauropods appeared about 160 million years earlier than
this fossil.

"We don't see much expansion of brain size in this group of
animals as they go through time, unlike a lot of mammalian and
bird groups, where you see increases in brain size over time,"
researcher Lawrence Witmer, an anatomist and paleontologist at
Ohio University, told LiveScience. "They apparently hit on
something and stuck with it — expansion of brain size over time
wasn't a major focus of theirs."

For years, scientists have wondered how the largest
land animals ever lived with such tiny brains. "Maybe we
should flip that question on their end — maybe we shouldn't ask
how they could function with tiny brains, but what are many
modern animals doing with such ridiculously large brains. Cows
may be triple-Einsteins compared to most dinosaurs, but why?"
Witmer said.

Their computer model also revealed the ampelosaur had a small
inner ear.

"Part of the inner ear is associated with hearing, so the fact it
had a small inner ear means it probably wasn't all that good at
hearing airborne sounds," Witmer said. "It probably used a kind
of hearing we don't think much about, which depends on sounds
transmitted through the ground."

The inner ear is also responsible for balance and equilibrium,
Witmer said.

"Given what we know about its inner ear, Ampelosaurus
probably didn't put a real premium on rapid, quick jerky eye or
head movements, which makes sense — these are relatively large,
slow-moving, plant-eating animals," he said.

Knoll and his colleagues had previously developed 3-D
reconstructions of another sauropod, Spinophorosaurus
nigeriensis. In contrast to Ampelosaurus,
Spinophorosaurus had a fairly developed inner ear.

"It is quite enigmatic that sauropods show such a diverse inner
ear morphology whereas they have a very
homogeneous body shape," Knoll said. "More investigation is
definitely required."

Currently scientists are debating whether sauropods held their
heads near the ground, grazing on low vegetation, or high up like
giraffes to browse on high leaves. "It could be that learning
more about the inner ear could tell us what sauropod neck posture
was like," Witmer said.

The scientists detailed their findings online Jan. 23 in the
journal PLOS ONE.